Positive displacement piston pump, for lubication

ABSTRACT

A positive displacement pump whose structure allows to increase the pressure of the lubricant taken from the oil sump, wherein the free level surface of the lubricant could even be located far away from the rotating members of the machine. This applies specifically to reciprocating, air compressors, which generally have an oil sump arranged very distant from the drive shaft used to transmit the motion needed for the actuation of the pump. The pump is based on a crank mechanism (7, 7′, 7″; 13; 13′) that sucks the lubricant and delivers it under pressure, in a target-oriented manner, to the components which require lubrication.

TECHNICAL FIELD

The device of the present invention is applicable, although not exclusively, to the field relating to the lubrication of mechanical components of reciprocating compressors and of small-sized internal combustion engines. In order to supply the necessary amount of liquid lubricant in the above machines, lubrication systems are required that are capable of handling even very modest lubricant flow rates and to supply them to the required points; moreover, said systems should have a simple mechanics, be realizable at low cost, and be able to utilise the motion provided by the machine on which they are mounted, without resorting to unduly complicated mechanisms (like additional small shafts, power takeoffs, etc.).

BACKGROUND ART

At present, lubrication in small-sized piston engines and in reciprocating compressors is performed substantially either by splash lubrication, in case this method is considered satisfactory, or by employing gear pumps, in case the needs of a good lubrication are more pressing. Recently, mechanically actuated (usually by a cam), small-sized, positive displacement pumps have also been developed, as well as electromagnetically controlled valves, specifically for small internal combustion motors of motorcycles or scooters.

Splash lubrication, which relies on the splashing and agitation caused by the very components to be lubricated (which are wetted by the oil generally contained inside an oil sump), has the advantage to be extremely economical and simple, provided it is able to insure a sufficient lubrication. Nevertheless, it has considerable drawbacks, like the need to maintain a constant lubricant level inside the oil sump in order to avoid seizure, the fact that the lubricant is not accurately supplied only to the points were it is really needed, the fact that it is impossible to supply the lubricant under pressure, the impossibility of using this kind of system in two-stroke engines with dry sump oil pumps, since in these applications the sump oil pump must work under dry conditions. Lubrication under pressure has become the mostly used system because of its undoubted advantages linked to its utilisation, these advantages being, among others, the increase of the performance of the kinematical couples lubricated under pressure as compared with that obtainable without the contribution of the feed pressure. In particular, the lubrication relying on gear pumps has the advantage of putting under pressure the lubrication circuit and of allowing to accurately reach the various points or areas to be lubricated, with the required oil flow rate and the correct (prescribed) pressure value.

In this case, the lubricant also has the not negligible task of cooling the surfaces which are in mutual contact. Also the use of cam-actuated positive displacement pumps has quickly become widespread, besides that of electromagnetic pumps, in the field of small-sized internal combustion engines and in the technical field of compressors, due to the possibility of feeding the lubricant under pressure, by controlling the flow rates, and therefore, taking advantage of the possibility of cooling down the various lubricated kinematical couples. However, the inconvenience of the utilisation of gear pumps lies in the increased costs involved in the production of high-quality mechanical components, like gearwheels for instance, and in the need to provide an adequate power takeoff (drive), so that the machine to be lubricated is more difficult to manufacture. On the other hand, the drawbacks of utilising cam-actuated pumps, in their commonly used version, are the requirement of their assembling in the vicinity of the driving shaft and the need of having available an adequate oil level in the oil sump in order to permit the priming (pump starting). Moreover, the disadvantages of using electromagnetically controlled pumps are generally the increased production cost, the electric power absorption, and the necessity of providing a control unit.

BRIEF DESCRIPTION OF DRAWINGS

The invention will now be described for illustrative purposes only having regard to three of its possible embodiments, which are neither limitative nor binding, and which are depicted in the annexed drawings, in which:

FIG. 1 shows the first embodiment of the needle-shaped positive displacement pump according to the present invention;

FIGS. 2 a and 2 b are two orthogonal views of the second embodiment of the needle-shaped positive displacement pump according to the present invention;

FIGS. 3 a and 3 b are two orthogonal views of the third embodiment of needle shaped positive displacement pump according to the present invention.

DESCRIPTION OF THE INVENTION AND OF ITS PREFERRED EMBODIMENTS

The present invention suggests a valid alternative to conventionally used arrangements in the field of lubrication systems for small-sized, internal combustion motors, and for positive displacement compressors. In substance, it consists of a piston pump whose structure, however, is such as to permit to put under pressure the lubricant taken from the oil sump, wherein, the free, upper surface of the oil level may also be located far away from the rotating members of the machine. This holds in particular in an application concerning air compressors of the reciprocating kind, which generally have an oil sump located somewhat distant from the driving shaft from which it is possible to draw the motion for the actuation of the pump. FIG. 1 shows a schematic cross-section of a possible embodiment of the present invention, formed by:

-   a cylinder body 1; -   a piston (plunger) 2; -   a check valve 3; -   a suction duct 4; -   a link rod 5; -   a plug 6; -   a crank 7.

The operation of this system—called “A-version”—, shown in FIG. 1, is as follows: The crank 7, by rotating around its own axis, gives rise to a relative motion—by means of the link rod 5—between the piston 2 (which is hinged at the eccentric hole of the crank) and the cylinder body 1. This motion is the classical reciprocating motion of a conventional crank mechanism, whose stroke equals twice the distance between the axis of the crank 7 and the axis X of the eccentric hole of the crank 7. Starting from the bottom dead centre (BDC), the piston 2, while moving upwards, generates a negative pressure inside the cylinder 1, which is due to the fact that there is no fluid communication to the outside environment, because the suction inlet 10 remains closed (obstructed) by the piston 2 itself, while the delivery is controlled by the check valve 3. When the piston 2 opens the suction inlet (suction opening) 10 obtained in the cylinder 1, lubricant is sucked through the suction inlet 4 immersed in the lubricant (this system is self-starting or “self-priming” provided the negative pressure obtained inside the cylinder 1 insures the lifting of the liquid from the free, upper surface level, up to the suction opening 10). Upon reaching the top dead centre (TDC), the piston 2 inverts its direction of motion; there will be a first phase of backflow of lubricant through the suction inlet, but then, after the piston 2 has closed this inlet 10, the delivery phase starts, after the opening of the check valve 3 under the pressure force exerted by the compressed lubricant—on this check valve 3—, which overcomes the closure force of the spring 11 of the valve 3. Thus, the lubricant first flows past the check valve 3 and then through a cavity obtained in the piston 2, until it reaches a delivery region. The plug 6 exerts a backing function (abutment) on the closure spring 11 of the check valve 3. The flow rate (delivery or capacity) of the pump of the invention can be modified by selecting an adequate cylinder bore or a suitable stroke (eccentricity of the hole on the crank).

In FIG. 2 there is shown a further version (embodiment) of the small pump according to the present invention, that will be named “B-version”. This system comprises:

-   a cylinder body 1′; -   a piston or plunger 2′; -   a check valve 3′; -   a small, flexible delivery tube (small delivery hose) 4′; -   a crank 7′; -   a pressure-relief valve 8′ (optional).

In FIG. 1, and in the following figures, “X” always denotes the axis of the eccentric bore of the crank 7′ and “Y” the axis of the driving shaft 13.

The operation of the system illustrated in FIG. 2 (a and b) is basically the same as that of the device named “A-version”, with the only difference that the lubricant is now compressed inside a cylinder body 1′, which is substantially completely dipped (immersed) in the lubricant, while it is supplied to the delivery region through an additional element forming essentially a small hose 4′. The operation is detailed in the following paragraph:

The crank 7′, while rotating around its axis, brings about a relative motion between the piston 2′ (hinged on the eccentric bore 9′ of the crank; X-axis) and the cylinder body 1′, the latter being hinged (at 15′) to the oil sump (not shown). The resulting motion is a classical reciprocating motion of a conventional crank mechanism whose stroke is twice the distance existing between the axis of the crank 7′ and the axis X of the eccentric bore 9′ of the crank 7′. Starting from the BDC, the piston 2′, in the course of its upward motion, generates a negative pressure inside the cylinder 1′ which is due to the fact that there is no fluid communication to the outside because the suction inlet (analogous to 10 of FIG. 1 but not shown in FIGS. 2 a, 2 b) is closed by the piston itself and the delivery is controlled by the check valve 3′. When the piston 2′ opens said suction inlet obtained in the cylinder 1′, lubricant is sucked through this suction inlet, which is immersed in the lubricant (this system, obviously, is always self-starting or “self priming”). Upon arriving at the TDC (top dead centre) the piston 2′ inverts its direction of motion; there will be a first phase of backflow through the suction inlet, and then the delivery phase will start after the piston 2′ has closed said inlet and the check valve 3′ has opened under the pressure force exerted—on this check valve 3′—by the compressed lubricant, this pressure force overcoming the closing force of the spring (not shown in FIG. 2) of the valve 3′. The lubricant, after flowing beyond the check valve 3′, will flow through the small hose 4′ and will finally reach the delivery zone after having passed through a plurality of passages 9′ and 12′, thereby effecting eventually an accurate lubrication at the desired points (the components that need to be lubricated are not shown in the drawings). In this version, the problem of connecting the pumping zone with the delivery zone, which are in relative motion, is solved by using a flexible tube 4′.

This system may be equipped with a pressure-relief valve 8′.

In the “C-version” corresponding to the third embodiment according to FIG. 3, the system includes:

-   a cylinder body 1″; -   a piston or plunger 2″; -   a check valve 3″; -   a rigid, delivery duct 4″; -   a crank 7″; -   an element 14″; -   a pressure-relief valve 8″.

The operation of the system named “C-version” (third embodiment) is identical with the device named “B-version” (second embodiment) except that the lubricant arrives at the delivery zone by passing through an additional, rigid duct 4″. In this version, the problem of connecting together the pumping zone with the delivery zone, which are in relative motion to each other, is solved by using a cylindrical rigid element 4″ (rigid duct) that slides within the piston-bearing body 14″. In this case too, the system may be equipped with a pressure-relief valve 8″.

Obviously, also in the third embodiment of FIG. 3 (a and b), the pivoting point (pivot pin) 15″ is hinged to the oil sump (not shown). 

1-9. (canceled)
 10. A positive displacement piston pump, for performing a target-oriented lubrication, comprising a crank mechanism (7; 13), which for its motion takes directly advantage of the motion of a drive shaft (13) to suck and compress a lubricant, characterized in that it comprises: a cylinder body (1) pivoted to an oil sump and receiving a sliding piston (2); a check valve (3); a suction duct (4) located in the lower part of said cylinder body (1), a link rod (5) interconnecting said piston (2) and said cylinder body (1); a crank (7) rigidly and eccentrically coupled with said drive shaft (13).
 11. A positive displacement piston pump according to claim 10, characterized in that only the suction duct (4) is at least partially located below the free upper surface level of lubricant introduced inside the oil sump.
 12. A positive displacement piston pump according to claim 10, characterized in that it includes a pressure-relief valve.
 13. A positive displacement piston pump according to claim 11, characterized in that it includes a pressure-relief valve.
 14. A positive displacement piston pump according to claim 10, characterized in that the check valve (3) has a spring (11) whose preloading is adjustable by means of a regulation plug (6) located inside the piston (2).
 15. A positive displacement piston pump according to claim 11, characterized in that the check valve (3) has s spring (11) whose preloading is adjustable by means of a regulation plug (6) located inside the piston (2).
 16. A positive displacement piston pump, for performing a target-oriented lubrication, comprising a crank mechanism (7′, 7″; 13′), which for its motion takes directly advantage of the motion of a drive shaft (13′) to suck and compress a lubricant, characterized in that the lower part of the pump forms a cylinder body (1′; 1″) which is substantially totally immersed in the lubricant and which is pivotally connected (15′; 15″) to an oil sump, a piston (2′; 2″) sliding inside said cylinder body (1′; 1″) and performing a reciprocating motion originated by said crank mechanism (7′ 7″; 13′), and said cylinder body (1′; 1″) being internally provided with a check valve (3′; 3″) and with a connection to a delivery tube (4′; 4″) of the lubricant.
 17. A positive displacement piston pump according to claim 16, characterized in that a pressure-relief valve (8′; 8″) is also provided inside said cylinder body (1′; 1″).
 18. A positive displacement piston pump according to claim 16, characterized in that said delivery tube (4′) for supplying the lubricant is flexible.
 19. A positive displacement piston pump according to claim 17, characterized in that said delivery tube (4′) for supplying the lubricant is flexible.
 20. A positive displacement piston pump according to claim 16, characterized in that said delivery tube (4″) for supplying the lubricant is rigid and slides inside an element (14″) which is connected with said crank (7″) of said crank mechanism.
 21. A positive displacement piston pump according to claim 17, characterized in that said delivery tube (4″) for supplying the lubricant is rigid and slides inside an element (14″) which is connected with said crank (7″) of said crank mechanism. 